black smoke and possible missfire



hi all if anyone can help please.
i have a 2001 ml270 cdi and its started black smoking bad.
i have replaced all 5 injectors and 5 glow plugs....had some fun helli coiling on 3 injectors!!but done it
never fails to start just a bit lumpy on revs but can rev through it.
the more steady high revs the smoke clears up.
checked turbo/waste gate.and intercooler......moved on to egr,removed it and was stuck shut so cleaned it and tested that vacuum was opening it ok.
the boost pipe from intercooler to egr brings in good strong air on tick over but when you give it a little throttle the air stops from turbo as egr opens and brings in exhaust gases for inlet...then egr closes and air from turbo starts this normal?.
i am suspecting that too much diesel and not enough air hence the black smoke,so today i removed the inlet manifold....was expecting chambers to be blocked but seems clear ,,,needed a good clean though, which i have done with a good blast from the pressure wash too ,checking the flow,also checked the flaps are working and intacted ok so my question is while all this is out is there anything else i can check before i put inlet back in.
i have had 5 ml270's and this is the first that has given a problem and dont believe the engine is knackered....can anyone shed any light please
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